Heavy media separation and analysis

Simplified heavy media separation method.

Heavy media separations (HMS) are commonly used in the geosciences to divide crushed rocks or soils into their respective light and heavy specific gravity fractions e.g. gold panning where water provides the medium and the panning action separates the denser gold particles from the lighter, gangue minerals. In the laboratory, HMS are often employed to separate mineral grains prior to further analysis.

The separated heavy minerals provide important indicators of sedimentary rock provenance, sediment pathways and palaeogeography and the degree of diagenesis that sediments have undergone. They may also enable stratigraphic correlation and are particularly useful where biostratigraphic information is absent.

Separation

Traditionally, the heavy media employed were halogenated organic solvents (e.g. bromoform, methylene iodide and tetrabromoethane) but these are highly toxic, require strict Health and Safety protocols and are increasingly difficult to obtain.

BGS have therefore researched and replaced halogenated organic solvents with lithium polytungstate (LST) media which offer the following advantages:

non-toxic

can be used in open vessels without the need for forced extraction or specialised personal protective equipment

cheaper, as LST is 99% recoverable

specific gravity can be simply adjusted by adding or removing deionised water